With the advent of increasing activity in aquaculture or fish farming in the early to mid-1980s, research has been ongoing into increasing productivity or growth rate and reducing the mortality rate of fish raised in aquaculture conditions since survival of such fish is important. One such factor relates to enhancing the nutritional value and palatability of feed used in raising such fish. In addition to the nutritional value, it is desirable to reduce the cost of feed to such fish since, typically, the feed totals approximately 40 to 50% of the cost of raising the fish. Such feed should be a high quality feed to meet the objectives of having high nutritional value to maximize growth and to reduce fish mortality.
The requirement for feed products in aquaculture is projected to grow substantially and, as a result, there is and will be pressure to obtain the necessary ingredients for fish food. The possibility of using zooplankton and, in particular, euphausiids, as a fish feed, appetizer or food product has been investigated and has been found to be possible and desirable, particularly as a feed product. Euphausiids are a natural feed harvested directly from coastal waters and have a high nutritional value but, previously, the cost of harvesting and processing such zooplankton for a feed product has been prohibitively expensive.
As well, the questions of the availability of the biomass of such zooplankton, storage of the zooplankton and its harvesting and processing are parameters that must be investigated in order to determine whether the product would be appropriate as a feed product.
Through papers written by Fulton and other authors, the use of zooplankton as a food or feed product has been contemplated for some time. In particular, antarctic krill (Euphausia superba) for human consumption have been investigated, although relatively little work has been investigated related to aquaculture. The use of Euphausia pacifica in the coastal waters of British Columbia, Canada has been considered in relation to aquaculture only.
It appears, from those investigations, that the necessary biomass is available in coastal waters. Previously, euphausiids have been used as a pet food ingredient and some aquaculture operators have used euphausiids as a feed product. The euphausiids were used for such purposes in a frozen form after being harvested and in some cases, the euphausiids were freeze dried following harvesting. This is an expensive procedure.
Harvesting euphausiids from coastal waters was previously done utilizing a mid-water trawl. When the trawl net was full of euphausiids, the trawl net would be raised and the euphausiids would be stored on a shipboard location for subsequent freezing. In utilizing the mid-water trawl net, however, severe damage was caused to the euphausiids by being bunched in the cod end of the net. The euphausiids would end up being squashed and leaching action would occur when the net was raised which is believed to reduce the nutritional value of the euphausiids. To reduce this damage, only a certain weight of euphausiids were subsequently taken in each operation when raising the net in an attempt to reduce the handling damage. Nevertheless, a certain degree of damage still occurred and, of course, the time required to raise the net is a disadvantage because of the reduction of fishing time.
In processing feed products, it has typically been the case that the ingredients used in such feed products are heated to a high temperature around 100.degree. C. when the product is processed and dried. By heating the product to such a high temperature, it is believed that the enzymes and other proteins in the product are denatured. If, however, it is intended to utilize the product for early stage or juvenile aquaculture, which young fish have relatively undeveloped digestive systems, it is believed to be desirable that the euphausiids maintain a certain proportion of enzymes which will assist the digestive process in such larvae. If the theory that enzymes are advantageous in nutrition is correct, such destruction of the enzymes during the aforementioned drying process is disadvantageous.
It is also desirable to have a natural product, where the proteins are not denatured, available for early stage juvenile or larvae feed. In some previous products, exogenous enzymes have been added to the zooplankton mix. However, the addition of such enzymes is difficult to control and can result in a complete hydrolysis of the proteins to amino acids. The presence of free amino acids in the feed needs to be controlled since they can create an inferior product of substantially reduced value for a feed product.
It has been shown, surprisingly, that the degree of enzyme activity which results in determining the digestibility of a product, reaches a relatively constant value after a certain period of time in a natural product. Recent investigations conducted by the applicant have confirmed this characteristic for Euphausia pacifica. This characteristic was first discovered in relation to Euphausia superba by Kubota and Sakai in a report entitled "Autolysis of Antarctic Krill Protein and Its Inactivation by Combined Effects of Temperature and pH", Transactions of the Tokyo University of Fisheries, number 2, page 53-63, March 1978. However, the antarctic krill study done by Messrs. Kubota and Sakai had the objective of limiting enzyme activity which was deleterious to obtaining a food as opposed to a feed product. Messrs. Kubota and Sakai wished to inhibit the enzymatic activity by certain processing techniques which they considered desirable when the product was intended as a food product.
When a degree of stabilization in enzymatic activity has been obtained during the digestive process in the euphausiids, further processing may take place in order to make a useful product for commercial feed. Such processes may include adding acid to obtain an acid stabilized product or drying the product using a variety of drying techniques such as freeze drying, spray drying, or vacuum and air drying. Spray drying, as well as other drying processes, however, are done at temperatures that will permanently inactivate the enzymes in the euphausiids which, as earlier mentioned, is considered to be undesirable for aquaculture purposes although it is acceptable for purposes where the product is intended to be used as a carotenoid biopigment for coloring purposes in both feed and food products.